1. Field of the Invention
The present invention generally relates to a radio receiver system with a shared low noise amplifier in a multi-standard operation.
2. Background Art
Numerous wireless standards are available today for wireless networks and devices. These multiple standards can often operate in the same frequency bandwidth, but have different applications and uses. For example, both WLAN and Bluetooth operate in the same relative frequency space defined by the IEEE ISM band. Accordingly, a single receiver front-end can be used to support multiple radio standards. For example, both Bluetooth and WLAN (IEEE 802.11) can be processed using a common analog receiver front-end because their frequencies of operation are sufficiently close to each other. In a conventional receiver system, it is desirable to use a single antenna to support multiple radio standards to reduce part count and overall size.
FIG. 1 illustrates a conventional receiver system 100 that supports two radio standards, namely WLAN 802.11 and Bluetooth, using a single antenna. The conventional system 100 includes a single antenna 102, a power splitter 104, and two low noise amplifiers (LNA) 106 and 108. The power splitter 104 is used after the antenna 102 to provide the received signal to each one of the LNAs 106 and 108 for processing according to each standard, while maintaining the proper 50 ohm terminations on all ports. This results in a significant amount of signal power loss as seen by each one of the LNAs, even if no signal is being received for one of the standards. The signal power loss occurs because the power divider outputs are 3 dB lower than the input power. For example, in a system that is required to operate for both Bluetooth and WLAN in a single antenna configuration, a minimum of a 3 dB power penalty (and therefore noise figure [NF] penalty) occurs regardless of which standard is selected to receive the input signal.
Therefore, what is needed is receiver front-end apparatus that includes a single antenna that can also serve multiple standards without the above mentioned limitations.